apparmor: cleanup add proper line wrapping to nulldfa.in

nulldfa.in makes for a very long unwrapped line, which certain tools
do not like. So add line breaks.

Signed-off-by: John Johansen <john.johansen@canonical.com>

apparmor: add a default null dfa

Instead of testing whether a given dfa exists in every code path, have
a default null dfa that is used when loaded policy doesn't provide a
dfa.

This will let us get rid of special casing and avoid dereference bugs
when special casing is missed.

Signed-off-by: John Johansen <john.johansen@canonical.com>